Chagas disease occurs as a chronic infection in about 8-10 million people worldwide, almost all in Latin America (where the disease originated). Central America alone has 11 percent of the cases on the entire continent, but as a result of migratory flows to the rest of the world, over 300,000 cases are estimated in North America, 80,000 in Europe, 3,000 in East Asia, and 1,500 in Australia. Control efforts in the southern end of the Americas have had extremely positive effects, with Argentina, Chile, Brazil, Paraguay, and Uruguay reporting major declines in the number of cases.The image below depicts the global incidence of carriers infected with T cruzi.
(From Coura-Rodrigues J, Albajar-Vinas P. Chagas disease: a new worldwide challenge. Nature 2010; 465: S7;).
Because clinical infection with T. cruzi causes minimal symptoms, it is difficult to diagnose and is almost never treated, particularly in developing countries.
The incubation period typically lasts about a week. After this period, the disease develops into two stages, acute and chronic.
In the acute stage, which lasts for weeks or months (average duration is around two months), most people have no symptoms, or symptoms that are extremely mild and tend to resolve on their own (however, they can be fatal in children and immunocompromised individuals) such as:
- Fever;
- Headaches;
- Swollen lymph nodes;
- paleness;
- Muscle aches;
- difficulty breathing;
- abdominal and chest pain.
At this stage there is a high presence of parasites in the blood, which as trypomastigotes go on to invade the liver, intestines, spleen, lymphatic ganglia, central nervous system, and skeletal and cardiac muscles, where they take the form of amastigotes and cause a local inflammatory reaction. Because many of the symptoms are generally difficult to identify, the disease often goes undiagnosed. The parasite then enters a chronic phase, in which its presence in the blood is very low and becomes essentially undetectable. In most cases the disease never re-emerges (indeterminate form), but it is possible that after a period of time of 10 to 20 years after the acute infection, symptoms of this new phase will return. Thirty percent of people develop heart problems, which can even result in fatal arrhythmias. In 10% of cases, however, there are problems related to the digestive system, particularly the esophagus and colon.
Diagnosis of Chagas disease is problematic because screening is neither mandatory as part of the immigration process nor recommended by the American Academy of Pediatrics.
Multiple diagnostic, cultural, and economic barriers limit the diagnosis and treatment of Chagas disease.In particular, a University of Texas Chagas disease screening project focused on the Rio Grande Valley found significant technical problems due to the lack of specificity of available diagnostic tests.
In industrialized countries, diagnostic methods such as:
- Light microscopy of blood smears (thick drop or thin smear) or tissue (acute Chagas disease);
- Serological screening test confirmed by a second test;
- Polymerase chain reaction-based tests.
Treatment of infected infants and children
Cases of congenital T. cruzi infection should be treated as soon as the diagnosis has been confirmed. Current experience of clinical groups experienced in treating congenital T. cruzi infection confirms that both benznidazole (BZ) and nifurtimox (NF) can be used to treat congenital cases. The treatment is highly effective with fewer adverse events than those described in adults. Cure rates, as assessed by conventional serology, are greater than 90% in infants treated during the first year of age. Follow-up of treatment is recommended by parasitological or molecular testing in the weeks following the start of treatment for infants who manifest the presence of the parasite. After completion of treatment, patients should be followed up every 6 months with quantitative serologic testing: the patient is considered cured when the test becomes negative.
Treatment of infected girls or adults
Even in the more adult population, patients infected with T. cruzi should be treated with benznidazole (BZ) or nifurtimox (NF) according to WHO standard recommendations. However, antiparasitic treatment is contraindicated during pregnancy because the risks of using the available BZ and NF drugs on the fetus are unknown and the risk of adverse reactions is higher in adults. Therefore, infected mothers will be treated after delivery and the lactation period to avoid the interruption of lactation as a result of such possible adverse reactions.